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Corneal Physician

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Keratoprosthesis Options and Management

Several devices are available for high-risk corneas, and you can manage possible related complications

By: Matias Soifer, MD, Victor L. Perez, MD, Hazem M. Mousa, MD
Corneal Physician April 1, 2021 Vol 25, Issue April 2021 Page(s): 32-34, 36

Keratoprosthesis (KPro) is ideal for corneas that have extensive areas of vascularization, and/or have had multiple previous transplant failures, limbal stem cell deficiencies with or without cicatrizing conjunctivitis in the setting of an autoimmune disorder, or chemical injuries. The reason: These high-risk corneas represent the highest risk of failure with a standard PK. In fact, the presence of these characteristics can be associated with rates of allograft failure of up to 70% at 10 years.1,2 However, the survival prognosis for KPro varies, with better survival in cases of corneal allograft failure, and the worst prognosis in autoimmune-related, cicatricial, keratoconjunctival scarring, such as in Stevens-Johnsons syndrome or ocular cicatricial pemphigoid.3–5 Therefore, patient selection is crucial to ensure the benefits of KPro outweigh the risks.

Here, we discuss individual KPro devices and how to manage possible related complications.

KPro Devices

  • Boston Keratoprosthesis Type 1. This device is comprised of a collar button-shaped polymethyl methacrylate (PMMA) with a titanium ring available in two versions, Type 1 (Figure 1) and Type 2. It works best in eyes that have a wet ocular surface. Cases such as a history of multiple failed corneal transplants with extensive corneal neovascularization, corneal opacities associated with limbal stem cell deficiency syndromes, and mild-to-moderate chemical injury patients would be ideal candidates for this KPro.

     

    FIGURE 1: The back plate holes are shown to reduce corneal stromal melts.
    FIGURE 1: The back plate holes are shown to reduce corneal stromal melts.
    It contains several holes in the back plate, enabling continuous contact between the corneal stroma and the aqueous humor. This was shown to reduce the incidence of corneal stromal melts.6 In addition, the Boston Keratoprosthesis Type 1 has a titanium locking ring to prevent intraocular disassembly and promote an intact barrier against pathogens, and has a titanium backplate, demonstrating less formation of retro prosthetic membranes.7 Type 1 and Type 2 are available in either a pseudophakic power or customized aphakic power, the latter determined by the patient’s axial length. In addition, the back plate comes in adult (8.5 mm) and pediatric (7 mm) sizes. In eyes sans autoimmune diagnosis, the retention rate was 95.9% after one year, and 90.0% after two years post-implantation.8
  • Boston Keratoprosthesis Type 2. The Boston Type 2 KPro (Figure 2) is used in eyes that have end-stage ocular surface disease associated with significant conjunctival xerosis and keratinization, typically in the context of severe autoimmune disease.3 The procedure involves a complete tarsorrhaphy after which the optic is placed through an opening in the upper eyelid.9,10 The majority of reported cases treated with the Boston Type 2 KPro have involved Stevens-Johnson syndrome and ocular cicatricial pemphigoid, in which a visual acuity better than 20/50 was reported in 50% to 80% of treated patients.9-11

     

    FIGURE 2: Implanting this KPro involves a complete tarsorrhaphy.
    FIGURE 2: Implanting this KPro involves a complete tarsorrhaphy.
  • Modified Osteo-Odonto Keratoprosthesis (MOOKP). This KPro uses bone-tooth lamina to anchor a polymethyl methacrylate cylinder to the cornea12 (Figure 3). When adequately performed, it is recognized internationally as the provider of the best visual and retention results among the KPros.12,13 However, it remains an extremely difficult procedure that requires tedious planning, extensive training and the need for specialized centers.12–14 MOOKP is indicated in cases of bilateral blindness associated with significant conjunctival dryness and corneal diseases on which a conventional PK cannot be practiced.
      
    FIGURE 3: MOOKP is indicated for cases of bilateral blindness associated with significant conjunctival dryness and corneal diseases not suited for conventional PK.
    FIGURE 3: MOOKP is indicated for cases of bilateral blindness associated with significant conjunctival dryness and corneal diseases not suited for conventional PK.
    A contraindication is lack of suitable teeth, so investigators have tried to utilize other types of autologous tissues for this KPro, such as cartilage,15 and tibial bone.16,17
  • Moscow Eye Microsurgery Complex in Russia (MICOF) Keratoprosthesis. This KPro is comprised of a titanium skirt for implantation.18 In a two-stage procedure, the titanium frame is first implanted into the lamella of the cornea, and then the cornea is trephined inside the titanium ring, and the PMMA optic device is screwed in place of the trephined center.18,19 Patients with chemical injuries and autoimmune disorders have shown improvement with the use of this device.18,20,21 However, comprehensive data on the long-term success potential of this device are unavailable, necessitating close and long-term follow up.
  • KPros on the Horizon. Two devices are in the pipeline: (1) KeraKlear (KeraMed Inc.) is made of foldable, biocompatible artificial material and peripheral holes adapted for facilitated fixation into a corneal pocket.22 An incision is created with a femtosecond laser that results in a lamellar pouch, in which the KPro can then be folded and secured by anchoring sutures.22 It is commonly reserved for non-inflammatory corneal opacification disorders, such as keratoconus, corneal dystrophies and corneal scars, and its refractive power can be offered for phakic/pseudopakic and aphakic eyes. The entire procedure can be done with local anesthesia in a surgical suite. Data on the large-scale performance of this device on patients are limited. Complications potentially include risk of extrusion.22,23 (2) The expanded polytetrafluoroethylene (ePTFE) KPro involves the use of ePTFE, an inert vitreous Teflon alloplast that has high biocompatibility.24 It was recently evaluated on 19 rabbits that had no intraoperative complications, and a minority presented with infectious events or keratolysis. All devices remained in situ with clear optics without spoliation, demonstrating favorable short-term anatomical clinical outcomes.24 Further studies in humans are underway to reduce complications, improve clinical outcomes and define clinical indications, refractive power and size.

Managing Possible Related Complications

  • Glaucoma. Glaucoma is the most frequent cause of permanent blindness after KPro implantation, so patient selection is crucial. Digital palpation and scleral pneumatometry can be used to assess IOP in these patients, as these methods are not affected by the presence of the optic material.25 A future method of management could be IOP transducers with telemetry.26
  • Microbial keratitis. Postoperatively, the addition of a gram-positive antimicrobial to a fluoroquinolone in the postoperative management of KPro patients has reduced the rate of bacterial keratitis and endophthalmitis.27 A future method of management could be cross-linking for refractory bacterial keratitis and 5% povidone-iodine drops, with frequent replacement of the bandage contact lens every 2 months to reduce the risk of fungal infection.28 Patients with immune disorders are at higher risk for endophthalmitis than those with chemical burns.25 The overall prognosis after the occurrence of endophthalmitis is very poor. On the other hand, sterile vitritis has an excellent visual prognosis, although it is commonly managed initially as an endophthalmitis suspect.
  • Retroprosthetic membrane (RPM). A total pars plana vitrectomy (PPV), as opposed to a partial PPV during KPro implantation, reduces the incidence of the proliferation of fibrovascular tissue that grows behind the back plate of the device, occluding the internal surface of the optic, leading to decreased vision and possible angle-closure glaucoma.29 Likewise, titanium back plates reduced the incidence of PRM.6
  • Corneal melting. (Figure 4) Systemic anti-inflammatory medications, starting with steroids, with the possibility of escalating to a chimeric monoclonal antibody,30 may be used. When there is perforation, the only solution is surgical. A recent retrospective chart review of the Boston KPro patients with corneal melt suggested that surgical exchange for a new KPro may be a better choice to lower the risk of recurrence of melt and infection.31 Future methods of management include cross-linking to achieve increased corneal rigidity and reduced corneal melt. A multicentric, randomized clinical trial is currently underway comparing Boston KPro, with and without previous cross-linking of the donor cornea, to understand the possibility of preventing keratolysis and its subsequent complications (Clinical trial identifier: NCT02863809).

     

    FIGURE 4: Corneal melting is an example of a possible related complication of KPro. Treatment: systemic anti-inflammatory drugs, escalating to a chimeric antibody.
    FIGURE 4: Corneal melting is an example of a possible related complication of KPro. Treatment: systemic anti-inflammatory drugs, escalating to a chimeric antibody.

Meeting a Need

KPro is a fundamental resource for that subpopulation of high-risk corneal transplant patients who would otherwise end up in a vicious cycle of repeat keratoplasties, causing physician and patient frustration. That said, it is important to remember that KPro carries possible complications that need to be addressed via frequent clinical visits. Modifications to the current KPro devices are being constantly adapted to decrease these complications. CP

References:

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  12. Falcinelli G. Modified osteo-odonto-keratoprosthesis for treatment of corneal blindness: long-term anatomical and functional outcomes in 181 cases. Arch Ophthalmol. 2005;123(10):1319.
  13. Strampelli B. [OSTEO-ODONTOKERATOPROSTHESIS]. Ann Ottalmol Clin Ocul. 1963;89:1039-1044.
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  16. Charoenrook V, Michael R, de la Paz MF, et al. Osteokeratoprosthesis Using Tibial Bone: Surgical Technique and Outcomes. Ocul Surf. 2016;14(4):495-506.
  17. Temprano J. Tibial Bone KPro technique and long term results. Acta Ophthalmologica. 2009;87:0-0.
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  19. Avadhanam V, Smith H, Liu C. Keratoprostheses for corneal blindness: a review of contemporary devices. Clin Ophthalmol. 2015;9:697-720.
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  24. Akpek EK, Van Court S, Glass S, Schmiedel T, Troutman M. Short-Term Clinical Outcomes of a Novel Corneal Prosthetic Device in a Rabbit Model: Cornea. 2020;39(6):706-712.
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  26. Todani A, Behlau I, Fava MA, et al. Intraocular pressure measurement by radio wave telemetry. Invest Ophthalmol Vis Sci. 2011;52(13):9573-9580.
  27. Durand ML, Dohlman CH. Successful prevention of bacterial endophthalmitis in eyes with the Boston Keratoprosthesis: Cornea. 2009;28(8):896-901.
  28. De Oliveira LA, Magalhães FP, Hirai FE, De Sousa LB. Experience with Boston keratoprosthesis type 1 in the developing world. Can J Ophthalmol. 2014;49(4):351-7.
  29. Perez VL, Leung EH, Berrocal AM, et al. Impact of Total Pars Plana Vitrectomy on Postoperative Complications in Aphakic, Snap-On, Type 1 Boston Keratoprosthesis. Ophthalmology. 2017;124(10):1504-1509.
  30. Robert M-C, Črnej A, Shen LQ, et al. Infliximab after Boston Keratoprosthesis in Stevens–Johnson Syndrome: An Update. Ocular Immunology and Inflammation. 2017;25(3):413-417.
  31. Daoud R, Sabeti S, Harissi-Dagher M. Management of corneal melt in patients with Boston Keratoprosthesis Type 1: Repair versus repeat. Ocul Surf. 2020;18(4):713-717.

 

DR. SOIFER is a Cornea & Ocular Immunology Fellow and works in the Foster Center for Ocular Immunology at Duke Eye Center, in Durham, NC. Disclosures: None

 

 

DR. MOUSA works at the Foster Center for Ocular Immunology, Duke Eye Institute, and the Department of Ophthalmology, Duke University Medical Center, Durham, NC. Disclosures: None

 

 

DR. PEREZ is the director of the Foster Center for Ocular Immunology and director of the Ocular Surface program at Duke Ophthalmology. He spends 60% of his time researching ocular immunology and transplantation. Disclosures: Scientific advisor for Dompé and Alcon.

 

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